Method and system for time to first fix (TTFF) reduction of GPS receivers using satellite based augmentation system (SBAS) signal

ABSTRACT

A Global Positioning System (GPS) receiver, a control method of the GPS receiver, and a GPS system are provided, which are capable of reducing an initial position check time using an SBAS signal transmitted from a SBAS satellite. The control method of a GPS receiver includes receiving an SBAS signal from a SBAS satellite and calculating a satellite clock and a satellite position of the GPS receiver using the received SBAS signal. The SBAS signal may contain a difference value between the ephemeris data and the almanac data of the GPS satellite. The difference value between the ephemeris data and the almanac data may include a satellite clock difference value and a satellite position difference value for the GPS satellite. Accordingly, it is possible to acquire the current position and time information more quickly and accurately, by shortening the initial position check time using the difference value between the ephemeris data and the almanac data included in the SBAS signal.

BACKGROUND Technical Field

The present disclosure relates to a Global Positioning System (GPS)receiver, a control method of the GPS receiver, and a GPS system, andmore particularly, to a GPS receiver, a control method of the GPSreceiver, and a GPS system, which are capable of reducing an initialposition check time using a Satellite Based Augmentation System (SBAS)signal transmitted from a SBAS satellite.

Background Art

Generally, Unmanned Aerial Vehicle (UAV), sometimes called a “drone”,refers to an aircraft that is capable of flying without a pilot aboardaccording to a pre-programmed program to perform a designated mission,or autonomously flying while recognizing by itself the environment(e.g., obstacle or route).

Unlike general aircraft, the UAVs do not have space for pilots or safetydevices for the purpose of compactness and lightweight, and they arewidely used for information gathering and reconnaissance in places wherehuman access is difficult. For example, UAVs are used for variouspurposes such as meteorological observations, acquisition of aerialimaging of catastrophe and disaster areas that are difficult to access,power line inspections, and so on.

In order to fly the UAV, navigation equipment including an inertialnavigation system for attitude control and a Global Positioning System(GPS) for guiding the route is necessary. UAV may use GPS to determinethe current position, and conventionally, there is a problem that theTime to First Fix (TTFF), which is the time required at the initialtake-off of the UAV for receiving the GPS signal and determining thecurrent position, is lengthened.

The GPS receiver determines in advance which satellite signals can bereceived based on the latest almanac data, and receives ephemeris datafrom one of the satellites receiving the latest ephemeris data toestablish a clock synchronization with the satellites, and receives thesignal from the three or more other satellites to measure the distanceto each satellite and determine its own position.

The TTFF may vary by Factory Start, Cold Start, Warm Start, Hot Start,and so on, depending on whether or not the almanac data and theephemeris data are received after the GPS receiver is turned on. Amongthese, except for the case of Hot Start in which the GPS receiver isused again within a few minutes after turn-off, or the GPS receiver istemporarily unable to receive GPS satellite signals due to obstacles(buildings, tunnels, etc.), TTFF generally takes about 30 seconds to 15minutes when it is necessary to receive the almanac data and theephemeris data.

Thus, there is a problem that the time until the UAV is operated issignificantly delayed due to the TTFF.

Therefore, it is essential to develop a technique to shorten the initialposition check time by using the difference value between the ephemerisdata and the almanac data included in the SBAS signal, in order toreduce the operation time of the UAV and to quickly determine thelocation of the UAV in the event of an emergency. Also, in addition toUAVs, it is essential to develop associated technologies in areas whereit is necessary to shorten the time to determine the current positionupon GPS receiver turn-on.

SUMMARY

Accordingly, it is an object of the present disclosure to provide a GPSreceiver, a control method of the GPS receiver, and a GPS system, whichmay quickly and accurately acquire current position and time informationby shortening an initial position check time using an SBAS signalincluding a difference value between ephemeris data and almanac data.

Further, in addition to the objects explicitly mentioned, the presentdisclosure includes other objects that may be achieved from theconfiguration of the present disclosure described below.

In order to achieve the technical objects mentioned above, a controlmethod of a GPS receiver according to an embodiment of the presentinvention may include receiving an SBAS signal from a SBAS satellite andcalculating a satellite clock and a satellite position of the GPSreceiver using the received SBAS signal.

The SBAS signal may contain a difference value between the ephemerisdata and the almanac data of the GPS satellite.

The difference value between the ephemeris data and the almanac data mayinclude a satellite clock difference value and a satellite positiondifference value for the GPS satellite.

The satellite clock difference value between the ephemeris data andalmanac data for the GPS satellite may be calculated byΔT ^(j)(t ₀)=T _(E) ^(j)(t ₀)−T _(A) ^(j)(t ₀)  [Equation 1]

The satellite position difference value between the ephemeris data andalmanac data for the GPS satellite may be calculated byΔx ^(j)(t ₀)=x _(E) ^(j)(t ₀)−x _(A) ^(j)(t ₀)  [Equation 2]

where, t₀ is the time of calculating the satellite clock differencevalue at a ground station, ΔT^(j)(t₀) is the satellite clock differencevalue calculated at time t₀ at the ground station for j-th GPS satelliteamong a plurality of GPS satellites, T_(E) ^(j)(t₀) is the satelliteclock ephemeris data of the j-th GPS satellite, T_(A) ^(j)(t₀) is thesatellite clock almanac data of the j-th GPS satellite, Δx^(j)(t₀) isthe satellite position difference value calculated at time t₀ at theground station for the j-th GPS satellite among the plurality of GPSsatellites, x_(E) ^(j)(t₀) is the satellite position ephemeris data ofthe j-th GPS satellite, and x_(A) ^(j)(t₀) is the satellite positionalmanac data of the j-th GPS satellite.

The satellite clock ephemeris data of the GPS satellite may becalculated by{tilde over (T)} _(E) ^(j)(t)=T _(A) ^(j)(t)+ΔT ^(j)(t ₀)  [Equation 3]

The satellite position ephemeris data of the GPS satellite may becalculated by{tilde over (x)} _(E) ^(j)(t)=x _(A) ^(j)(t)+Δx ^(j)(t ₀)  [Equation 4]

where, t is the time of calculating the satellite clock ephemeris dataat a GPS receiver, {tilde over (T)}_(E) ^(j)(t) is the satellite clockephemeris data calculated at time t for a j-th GPS satellite, T_(A)^(j)(t) is the satellite clock almanac data already maintained in theGPS receiver at time t for the j-th GPS satellite, ΔT^(h)(t₀) is thesatellite clock difference value between the ephemeris data and thealmanac data acquired from a SBAS message for the j-th GPS satellite,{tilde over (x)}_(E) ^(j)(t) is the satellite position ephemeris datacalculated at time t for the j-th GPS satellite, x_(A) ^(j)(t) is thesatellite position almanac data already maintained in the GPS receiverat time t for the j-th GPS satellite, Δx^(j)(t₀) is the satelliteposition difference value between the ephemeris data and almanac dataacquired from the SBAS message for the j-th GPS satellite, and t₀ is thetime of calculating the satellite position difference value at theground station.

The SBAS signal may include a difference value in the position and adifference value in a time correction value for 4 or more GPSsatellites, by 50 bits per second or less.

The GPS receiver according to another embodiment of the presentdisclosure may include a receiver configured to receive the SBAS signalfrom the SBAS satellite and a controller configured to calculate thesatellite clock and satellite position of the GPS satellite using thereceived SBAS signal.

The ground station according to another embodiment of the presentdisclosure calculates a difference value between ephemeris data andalmanac data of the GPS satellite, and includes the calculateddifference value in a SBAS message and transmit the same to the SBASsatellite.

According to the present disclosure, there is an advantage that the GPSreceiver may acquire the current position and time information morequickly and accurately, thereby enabling quick operation, since theinitial position check time is shortened by using the difference valuebetween the ephemeris data and the almanac data included in the SBASsignal. In addition, there is no need for a separate receiver since theGPS receiver may receive the SBAS signal and there is also no spaceconstraint since the present disclosure may be used in all the spaceswhere the SBAS signal may reach.

In addition, it is possible to acquire the current position and timeinformation required in the field of UAVs for the initial takeoffquickly and accurately through the use of SBAS signal, and precisioncontrol the UAV is enabled. In addition, the present disclosure may beapplied in various fields in which position and time information arerequired. Meanwhile, the effects of the present disclosure are notlimited to those described above, and other effects that may be derivedfrom the constitution of the present disclosure described below are alsoincluded in the effects of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentdisclosure will become more apparent to those of ordinary skill in theart by describing in detail exemplary embodiments thereof with referenceto the accompanying drawings, in which:

FIG. 1 is a schematic block diagram of a GPS system according to anembodiment of the present disclosure;

FIG. 2 is a detailed block diagram of the GPS receiver shown in FIG. 1;and

FIG. 3 is a view provided to explain an operation process of the GPSsystem according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present disclosure will be described indetail with reference to the accompanying drawings so that those skilledin the art can easily carry out the present disclosure.

FIG. 1 shows a schematic diagram of a GPS system according to anembodiment of the present disclosure.

As shown in FIG. 1, the GPS system 1 includes a ground station 100, anSBAS satellite 200, and a GPS receiver 300.

The ground station 100 may include a reference station (notillustrated), a central station (not illustrated), a satellitecommunication station (not illustrated), and so on. Specifically, GPSsignals may respectively be received from the reference stationsdistributed over a wide area and navigation data and distancemeasurements may be generated and transmitted to the central station.The central station may use the information collected from the referencestations to generate correction information for correcting the orbit,clock error and ionospheric delay error for GPS satellite to be used forthe position calculation at the GPS receiver 300, and generate integrityinformation for determining presence/absence of abnormality in the GPSsignal, or the like. The correction information and the integrityinformation generated at the central station may be included in the SBASmessage and transmitted to the satellite communication station. Thesatellite communication station may then transmit the SBAS signalincluding the SBAS message to the SBAS satellite 200.

In this example, the SBAS (Satellite Based Augmentation System) refersto a satellite-based correction system that corrects GPS signal errorsand provides accurate position information through geostationarysatellites. The SBAS may correct GPS error at about 1 m-level.

The ground station 100 may calculate respective difference valuesbetween ephemeris data and almanac data for a plurality of GPSsatellites (not illustrated). The ground station 100 may then includethe calculated difference values between the ephemeris data and thealmanac data of the GPS satellite in the SBAS message and transmit it tothe SBAS satellite 200.

The ephemeris data of the GPS satellite represents very precise orbitand clock correction information of the GPS satellite and may be updatedapproximately every 5 hours. The GPS satellite completes transmission ofthe ephemeris data in approximately 30 seconds and continuesretransmitting it.

The almanac data of the GPS satellite represents the approximate orbitalparameter information of the GPS satellite and may be updated once in afew months. The GPS satellite completes transmission of the almanac datain approximately 30 seconds and continues retransmitting it.

The ground station 100 may receive the ephemeris data and the almanacdata from the GPS satellite and calculate the difference value betweenthe ephemeris data and the almanac data of the corresponding GPSsatellite based on the received data.

The difference value between the ephemeris data and the almanac data ofthe GPS satellite may include the satellite clock difference value andthe satellite position difference value.

The satellite clock difference values between the ephemeris data and thealmanac data of the GPS satellite may be calculated by Equation 1 below.ΔT ^(j)(t ₀)=T _(E) ^(j)(t ₀)−T _(A) ^(j)(t ₀)  [Equation 1]

where, t₀ is the time of calculating the satellite clock differencevalue at the ground station, ΔT^(j)(t₀) is the satellite clockdifference value calculated at time t₀ at the ground station for thej-th GPS satellite among a plurality of GPS satellites, T_(E) ^(j)(t₀)is the satellite clock ephemeris data of the j-th GPS satellite, andT_(A) ^(j)(t₀) is the satellite clock almanac data of the j-th GPSsatellite.

The satellite position difference value between the ephemeris data andthe almanac data of the GPS satellite may be calculated by Equation 2below.Δx ^(j)(t ₀)=x _(E) ^(j)(t ₀)−x _(A) ^(j)(t ₀)  [Equation 2]

where, t₀ is the time of calculating the satellite clock differencevalue at the ground is station, Δx^(j)(t₀) is a satellite positiondifference value calculated at time t₀ at the ground station for thej-th GPS satellite among a plurality of GPS satellites, x_(E) ^(j)(t₀)is the satellite position ephemeris data of the j-th GPS satellite, andx_(A) ^(j)(t₀) is the satellite position almanac data of the j-th GPSsatellite.

The SBAS satellite 200 may include an SBAS message, including thedifference value between the ephemeris data and the almanac data of theGPS satellite transmitted from the ground station 100, in SBAS signal,and transmit the SBAS message to the GPS receiver 300 in the servicearea.

The GPS receiver 300 may accurately determine its own position by usingthe GPS signal received from the GPS satellite and the SBAS signalreceived from the SBAS satellite 200.

In particular, the GPS receiver 300 according to the present disclosuremay calculate its own position even before acquiring the ephemeris dataand the almanac data, by receiving the GPS signal from the GPS satelliteupon turn-on.

The GPS receiver 300 may acquire the difference value between theephemeris data and the almanac data of the GPS satellite from the SBASsignal. The GPS receiver 300 may acquire the ephemeris data of the GPSsatellite by applying the difference value between the acquiredephemeris data and the almanac data to the previously stored almanacdata. This will be described in detail below.

FIG. 2 is a diagram showing a detailed configuration of the GPS receiverillustrated in FIG. 1.

The GPS receiver 300 may include a receiver 310, a controller 330 and astorage 350.

The receiver 310 may receive the SBAS signal from the SBAS satellite 200through the antenna.

The controller 330 may calculate the satellite clock ephemeris data andthe satellite position ephemeris data of the GPS satellite using thereceived SBAS signal. The information previously stored at the GPSreceiver 300 may be used for the almanac data.

More specifically, the controller 330 may calculate the satellite clockinformation and the satellite position information of the correspondingGPS satellite, using the difference value between the ephemeris data andthe almanac data of the GPS satellite included in the SBAS message.

Equation 3 below shows the calculation of the satellite clock ephemerisdata of the GPS satellite at the GPS receiver 300.{tilde over (T)} _(E) ^(j)(t)=T _(A) ^(j)(t)+ΔT ^(j)(t ₀)  [Equation 3]

where, t is the time of calculating the satellite clock ephemeris dataat the GPS receiver, {tilde over (T)}_(E) ^(j)(t) is the satellite clockephemeris data calculated at time t for the j-th GPS satellite, T_(A)^(j)(t) is the satellite clock almanac data already maintained in theGPS receiver at time t for the j-th GPS satellite, ΔT^(j)(t₀) is thesatellite clock difference value between the ephemeris data and thealmanac data acquired from the SBAS message for the j-th GPS satellite,and t₀ is the time of calculating the satellite clock difference valueat the ground station.

Equation 4 below shows the calculation of the satellite positionephemeris data of the GPS satellite at the GPS receiver 300.{tilde over (x)} _(E) ^(j)(t)=x _(A) ^(j)(t)+Δx ^(j)(t ₀)  [Equation 4]

where, t is the time of calculating the satellite position ephemerisdata at the GPS receiver, {tilde over (x)}_(E) ^(j)(t) is the satelliteposition ephemeris data calculated at time t for the j-th GPS satellite,x_(A) ^(j)(t) is the satellite position almanac data already maintainedin the GPS receiver at time t for the j-th GPS satellite, Δx^(j)(t₀) isthe satellite position difference value between the ephemeris data andthe almanac data acquired from the SBAS message for the j-th GPSsatellite, and t₀ is the time of calculating the satellite positiondifference value at the ground station.

The controller 330 may calculate the current position and timeinformation of the GPS receiver 300 using the satellite clock ephemerisdata and the satellite position ephemeris data of the GPS receivercalculated in the manner described above.

The controller 330 may store the calculated current position and timeinformation of the GPS receiver 300 in the storage 350 or may transmitit to a device (e.g., control means of UAV) connected to the GPSreceiver 300.

The storage 350 may store the almanac data received from the GPSsatellite and provide the almanac data when the controller 330calculates the ephemeris data using the difference value included in theSBAS signal.

Meanwhile, it is possible to include, by 50 bits per second or less, thedifference values between the ephemeris data and the almanac data for 4to 5 or more GPS satellites in the SBAS message and provide the SBASmessage.

More specifically, the transmission rate of the SBAS signal transmittedfrom the SBAS satellite 200 (i.e., transmission rate of the SBASmessage) is 250 bits per second, and the data field excluding thepreamble and the message ID is 212 bits. In the current standard SBASmessage format, the capacity available for the difference values betweenephemeris data and almanac data for the GPS satellites is 50 bits persecond. By loading the difference values between the ephemeris data andthe almanac data of the four or more GPS satellites on one SBAS message,which can be transmitted every 5 seconds, it is possible to shorten theinitial position check time to about 5 seconds.

The technique for shortening the initial position check time may beapplied to the field of UAVs or all technical fields associated withproviding position and time information using a GPS receiver. In thefield of UAVs, because the position and time information required at theinitial take-off can be acquired quickly and accurately through the SBASsignal, precision control of UAVs is enabled, and the performance ofvarious functions requiring the position and time information such asReady to Fly Mode, Return Home or Waypoint, and so on can also beenhanced.

In addition, other science fields of providing position information arealso applicable. For example, position information is necessary forinvestigating moving marine ecosystems such as whales, and so on, butsince the position information may not be obtained when the whalesubmerged in the sea, the position information should be acquired forthe time of about 30 seconds until the whales reappear on the surface ofthe water and the acquired position should be transmitted.

Therefore, if it is possible to shorten the initial position check timeand shorten the position information acquisition time, it will bepossible to track the movement of the whales more precisely and conductaccurate ecological investigation.

Hereinafter, a control method of a control system will be describedaccording to an embodiment of the present disclosure.

FIG. 3 is a view provided to explain an operation procedure of a GPSsystem according to an embodiment of the present disclosure.

As illustrated in FIG. 3, the ground station may calculate and transmitthe difference value between the ephemeris data and the almanac data ofthe GPS satellite to the SBAS satellite, at S300.

More specifically, the ground station may calculate the difference valuebetween the ephemeris data and the almanac data of the GPS satellitebased on the GPS satellite information generated from its constantobservation on the GPS signal and include the calculated result in theSBAS message and transmit this to the SBAS satellite.

At S300, the ground station may include, by 50 bits per second or less,the difference value between the ephemeris data and the almanac data for4 to 5 or less GPS satellites in the data field of the SBAS message andtransmit the SBAS message.

The SBAS satellite may then include the SBAS signal including thedifference value between the ephemeris data and the almanac data of theGPS satellite in the SBAS signal and transmit the SBAS signal, at S310.

The GPS receiver may then receive the SBAS message including thedifference value between the ephemeris data and the almanac data of theGPS receiver from the SBAS satellite, at S320. The operation at S320 maybe performed upon the GPS receiver being turned on, before receiving theGPS signal from the GPS satellite to acquire the ephemeris data.

The GPS receiver may then acquire the ephemeris data of the GPSsatellite using Equation 3 or 4 described above, using the differencevalue between the ephemeris data and the almanac data included in thereceived SBAS message, and may calculate its position and timeinformation using the acquired data, at S330.

Embodiments of the present disclosure include a computer-readable mediumincluding program instructions for performing variouscomputer-implemented operations. The medium records a program forexecuting the GPS receiving method described above. The medium mayinclude program instructions, data files, data structures, etc., aloneor in combination. Examples of such medium include magnetic medium suchas hard disks, floppy disks and magnetic tape, optical recording mediumsuch as CD and DVD, floptical disk and magneto-optical medium, hardwaredevices configured to store and execute program instructions, such asROM, RAM, flash memory, etc. Examples of program instructions includemachine language codes such as those generated by a compiler, as well ashigh-level language codes that may be executed by a computer using aninterpreter, and so on.

The present disclosure has been described in detail. However, it shouldbe understood that the detailed description and specific examples, whileindicating preferred embodiments of the disclosure, are given by way ofillustration only, since various changes and modifications within thescope of the disclosure will become apparent to those skilled in the artfrom this detailed description.

What is claimed is:
 1. A control method of a Global Positioning System (GPS) receiver, comprising: receiving a Satellite Based Augmentation System (SBAS) signal from a SBAS satellite; and calculating a satellite clock and a satellite position of a GPS satellite using the received SBAS signal, wherein the SBAS signal comprises a difference value between ephemeris data and almanac data of the GPS satellite, wherein the difference value between the ephemeris data and the almanac data comprises a satellite clock difference value and a satellite position difference value for the GPS satellite, wherein the satellite clock difference value between the ephemeris data and almanac data for the GPS satellite is calculated by: ΔT ^(j)(t ₀)=T _(E) ^(j)(t ₀)−T _(A) ^(j)(t ₀)  [Equation 1] and the satellite position difference value between the ephemeris data and almanac data for the GPS satellite is calculated by: Δx ^(j)(t ₀)=x _(E) ^(j)(t ₀)−x _(A) ^(j)(t ₀)  [Equation 2] where t₀ is the time of calculating the satellite clock difference value at a ground station, ΔT^(j)(t₀) is the satellite clock difference value calculated at time t₀ at the ground station for j-th GPS satellite among a plurality of GPS satellites, T_(E) ^(j)(t₀) is the satellite clock ephemeris data of the j-th GPS satellite, T_(A) ^(j)(t₀) is the satellite clock almanac data of the j-th GPS satellite, Δx^(j)(t₀) is the satellite position difference value calculated at time t₀ at the ground station for the j-th GPS satellite among the plurality of GPS satellites, x_(E) ^(j)(t₀) is the satellite position ephemeris data of the j-th GPS satellite, and x_(A) ^(j)(t₀) is the satellite position almanac data of the j-th GPS satellite.
 2. The control method of claim 1, wherein the calculating the satellite clock and satellite position of the GPS satellite using the received SBAS signal comprises calculating the satellite clock ephemeris data of the GPS satellite by: {tilde over (T)} _(E) ^(j)(t)=T _(A) ^(j)(t)+ΔT ^(j)(t ₀)  [Equation 3] and calculating the satellite position ephemeris data of the GPS satellite by: {tilde over (x)} _(E) ^(j)(t)=x _(A) ^(j)(t)+Δx ^(j)(t ₀)  [Equation 4] where, t is the time of calculating the satellite clock ephemeris data at a GPS receiver, {tilde over (T)}_(E) ^(j)(t₀) is the satellite clock ephemeris data calculated at time t for a j-th GPS satellite, T_(A) ^(j)(t₀) is the satellite clock almanac data already maintained in the GPS receiver at time t for the j-th GPS satellite, ΔT^(j)(t₀) is the satellite clock difference value between the ephemeris data and the almanac data acquired from a SBAS message for the j-th GPS satellite, {tilde over (x)}_(E) ^(j)(t) is the satellite position ephemeris data calculated at time t for the j-th GPS satellite, x_(A) ^(j)(t₀) is the satellite position almanac data already maintained in the GPS receiver at time t for the j-th GPS satellite, Δx^(j)(t₀) is the satellite position difference value between the ephemeris data and almanac data acquired from the SBAS message for the j-th GPS satellite, and t₀ is the time of calculating the satellite position difference value at the ground station.
 3. The control method of claim 1, wherein the SBAS signal comprises a difference value in the position, and a difference value in a time correction value, for 4 or more GPS satellites, by 50 bits per second or less.
 4. A GPS receiver, comprising: a receiver configured to receive a SBAS signal from a SBAS satellite; and a controller configured to calculate a satellite clock and a satellite position of a GPS satellite using the received SBAS signal, wherein the SBAS signal comprises a difference value between ephemeris data and almanac data of the GPS satellite, wherein the difference value between the ephemeris data and the almanac data comprises a satellite clock difference value and a satellite position difference value for the GPS satellite, wherein the satellite clock difference value between the ephemeris data and almanac data for the GPS satellite is calculated by: ΔT ^(j)(t ₀)=T _(E) ^(j)(t ₀)−T _(A) ^(j)(t ₀)  [Equation 1] and the satellite position difference value between the ephemeris data and almanac data for the GPS satellite is calculated by: Δx ^(j)(t ₀)=x _(E) ^(j)(t ₀)−x _(A) ^(j)(t ₀)  [Equation 2] where t₀ is the time of calculating the satellite clock difference value at a ground station, ΔT^(j)(t₀) is the satellite clock difference value calculated at time t₀ at the ground station for j-th GPS satellite among a plurality of GPS satellites, T_(E) ^(j)(t₀) is the satellite clock ephemeris data of the j-th GPS satellite, T_(A) ^(j)(t₀) is the satellite clock almanac data of the j-th GPS satellite, Δx^(j)(t₀) is the satellite position difference value calculated at time t₀ at the ground station for the j-th GPS satellite among the plurality of GPS satellites, x_(E) ^(j)(t₀) is the satellite position ephemeris data of the j-th GPS satellite, and x_(A) ^(j)(t₀) is the satellite position almanac data of the j-th GPS satellite.
 5. The GPS receiver of claim 4, wherein the controller calculates the satellite clock ephemeris data of the GPS satellite by: {tilde over (T)} _(E) ^(j)(t)=T _(A) ^(j)(t)+ΔT ^(j)(t ₀)  [Equation 3] and the controller calculates the satellite position ephemeris data of the GPS satellite by: {tilde over (x)} _(E) ^(j)(t)=x _(A) ^(j)(t)+Δx ^(j)(t ₀)  [Equation 4] where t is the time of calculating the satellite clock ephemeris data at a GPS receiver, {tilde over (T)}_(E) ^(j)(t) is the satellite clock ephemeris data calculated at time t for a j-th GPS satellite, T_(A) ^(j)(t) is the satellite clock almanac data already maintained in the GPS receiver at time t for the j-th GPS satellite, ΔT^(j)(t₀) is the satellite clock difference value between the ephemeris data and the almanac data acquired from a SBAS message for the j-th GPS satellite, {tilde over (x)}_(E) ^(j)(t) is the satellite position ephemeris data calculated at time t for the j-th GPS satellite, x_(A) ^(j)(t) is the satellite position almanac data already maintained in the GPS receiver at time t for the j-th GPS satellite, Δx^(j)(t₀) is the satellite position difference value between the ephemeris data and almanac data acquired from the SBAS message for the j-th GPS satellite, and t₀ is the time of calculating the satellite position difference value at the ground station.
 6. The GPS receiver of claim 4, wherein the SBAS signal comprises a difference value in the position, and a difference value in a time correction value, for 4 or more GPS satellites, by 50 bits per second or less.
 7. A ground station configured to calculate a difference value between ephemeris data and almanac data of a GPS satellite, and include the calculated difference value in a SBAS message and transmit the same to a SBAS satellite, wherein the difference value between the ephemeris data and the almanac data comprises a satellite clock difference value and a satellite position difference value for the GPS satellite, wherein the satellite clock difference value between the ephemeris data and almanac data for the GPS satellite is calculated by: ΔT ^(j)(t ₀)=T _(E) ^(j)(t ₀)−T _(A) ^(j)(t ₀)  [Equation 1] and the satellite position difference value between the ephemeris data and almanac data for the GPS satellite is calculated by: Δx ^(j)(t ₀)=x _(E) ^(j)(t ₀)−x _(A) ^(j)(t ₀)  [Equation 2] where t₀ is the time of calculating the satellite clock difference value at a ground station, ΔT^(j)(t₀) is the satellite clock difference value calculated at time t₀ at the ground station for j-th GPS satellite among a plurality of GPS satellites, T_(E) ^(j)(t₀) is the satellite clock ephemeris data of the j-th GPS satellite, T_(A) ^(j)(t₀) is the satellite clock almanac data of the j-th GPS satellite, Δx^(j)(t₀) is the satellite position difference value calculated at time t₀ at the ground station for the j-th GPS satellite among the plurality of GPS satellites, x_(E) ^(j)(t₀) is the satellite position ephemeris data of the j-th GPS satellite, and x_(A) ^(j)(t₀) is the satellite position almanac data of the j-th GPS satellite.
 8. The ground station of claim 7, wherein the ground station calculates the satellite clock ephemeris data of the GPS satellite by: {tilde over (T)} _(E) ^(j)(t)=T _(A) ^(j)(t)+ΔT ^(j)(t ₀)  [Equation 3] and calculates the satellite position ephemeris data of the GPS satellite by: {tilde over (x)} _(E) ^(j)(t)=x _(A) ^(j)(t)+Δx ^(j)(t ₀)  [Equation 4] where, t is the time of calculating the satellite clock ephemeris data at a GPS receiver, {tilde over (T)}_(E) ^(j)(t) is the satellite clock ephemeris data calculated at time t for a j-th GPS satellite, T_(A) ^(j)(t) is the satellite clock almanac data already maintained in the GPS receiver at time t for the j-th GPS satellite, ΔT^(j)(t₀) is the satellite clock difference value between the ephemeris data and the almanac data acquired from a SBAS message for the j-th GPS satellite, {tilde over (x)}_(E) ^(j)(t) is the satellite position ephemeris data calculated at time t for the j-th GPS satellite, x_(A) ^(j)(t) is the satellite position almanac data already maintained in the GPS receiver at time t for the j-th GPS satellite, Δx^(j)(t₀) is the satellite position difference value between the ephemeris data and almanac data acquired from the SBAS message for the j-th GPS satellite, and t₀ is the time of calculating the satellite position difference value at the ground station.
 9. The ground station of claim 7, wherein the SBAS signal comprises a difference value in the position, and a difference value in a time correction value, for 4 or more GPS satellites, by 50 bits per second or less. 